Flexural Modulus

Definition - What does Flexural Modulus mean?

The flexural modulus of a material is a physical property denoting the ability for that material to bend. In mechanical terms, it is the ratio of stress to strain during a flexural deformation, or bending. It is fundamentally equivalent to the elastic modulus of a material, which is a measure of a material’s elasticity, but the two properties commonly hold different values, particularly in polymeric materials.

Flexural modulus is tested from a 3-point analysis on a rectangular beam of the material, with width w and height h. A parameter L specifies the length between two support points placed on the bottom of the beam. A force, F, is applied on a point on the opposite side and in-between the two supports, which creates a displacement in the material called the deflection, d. With these parameters, the flexural modulus, Ebend, is calculated as units of force per area as follows:

Ebend = (L3F) / (4wh3d)

Flexural modulus is an important calculation for engineers and architects as it relates to the amount of weight a material can handle when used as a structural support.

Corrosionpedia explains Flexural Modulus

Flexural modulus is important in understanding the rigidity or stiffness of a material. Certain material applications may need strength and rigidity for structural support, while other applications may require flexibility in order to prevent damage during bending. As such, there are a few factors that modulate the flexural modulus of a material and understanding these factors aids in material development and choice.

The base flexural modulus of a base material is determined by the fundamental properties of the material. For example, in plastics, the type of polymer, molecular weight, thickness and shape all play a role in the flexibility. One way to modulate the flexibility is to add a fine mineral filler, such as talc powder to the plastic. Typically, adding these fine mineral fillers will increase the flexural modulus and stiffen the material. The ability for a mineral filler to modulate the flexural modulus is also dependent on the aspect ratio and particle size of the filler. Higher aspect ratio particles increase the flexural modulus of a material more so than lower aspect ratio particles. Decreasing particle size of a mineral additive may increase flexural modulus if the particle size aspect ratio increases during the particle size reduction.

It is important to note that flexural modulus is a useful measure for materials that do not break or rupture upon the applied stress. Brittle materials that break upon a certain level of force are better evaluated by flexural strength.